In recent years, as a filter for removing fine particles such as ions from water, other solutions, or gas, a molded filter body employing graphene in which fine water passage holes are formed has been used (Patent Literature 1).
In general, graphene is formed on a surface of copper foil or the like by a chemical vapor deposition (CVD) method (Patent Literature 2). Therefore, in the past, a process called transcription, in which graphene is transferred to a desired support when using the graphene as a molded filter body, was required (Patent Literature 3).
In a transfer process, polymethyl methacrylate (PMMA) is spin-coated on an exposed surface of the graphene formed on a copper foil to form a thin protective film and dried, and then the dried film is floated on a Cu etching solution heated to 50° C. with the copper foil facing downward, and the copper foil is removed.
Next, the thin film of PMMA and graphene is washed with ultrapure water, and is scooped up so as to be placed on a silicon substrate of which the surface has been hydrophilized.
After that, the thin film is scooped up with a desired support made of a resin or the like, and dried, and the protective film of PMMA is removed by repeating the acetone immersion and the IPA dipping alternately several times.
In the end, by drying the support and the graphene, the graphene was able to be transferred to the support.
In such a conventional transfer process, it takes time and labor together with the consumption of chemicals and the like, and the productivity was low.
Further, in a process of forming or removing a coating on a surface of a layer of graphene, and scooping up or detaching with a silicon substrate or the like, the extremely thin graphene was sometimes damaged.
In addition, conventionally, in order to form water passage holes in graphene, a method of heating in the air at a high temperature of around 300 to 500° C., or in a mixed gas of oxygen and inert gas (nitrogen, argon, helium, or the like) has been performed (Patent Literature 1).
However, in this method, not only the film resist supporting graphene is broken by heat, but also due to the hole boring by combustion reaction of graphite, it was difficult to control the reaction, and the sizes of the water passage holes to be formed in graphene were also uneven. Therefore, this method was unsuitable for use for a molded filter body requiring uniform water passage holes.
Further, cinders of a support such as a resin and the like generated during the combustion contaminate graphene, and sometimes deteriorated the performance of the molded filter body.
In addition, there was also an ion-selective filter using carbon nanotube (Patent Literature 4) or carbon nanohorn (Patent Literature 5) other than the graphene (hereinafter, the single-walled carbon nanohorn is abbreviated as SWNH).
As another method of forming water passage holes in the carbon nano-material, there was a method in which a nitrate is attached to a carbon nano-material as an oxygen supply measure, and holes are formed by heating in vacuum or inert gas at 300° C. (Patent Literature 6).